Radio circuit and method of operating same



1932- F. w. HOCHSTETTER 1,846,597

RADIO CIRCUIT AND METHOD OF OPERATING SAME Filed Dec. 4, 1929 avwewcoz fivderick -fi SE /Wis Gwyn W416 Patented Feb. 23, 1932 UNITED STATES FREDERICK W. HOGHSTETTER, OF CEITTSBURGH, PENNSYLVANIA RADIO CIRCUIT AND METHOD or OPERATING-SAME 7 Application filed December 4, 1929. Serial No. 411,409.

This invention relates in general to radio circuits "and the method of operating the same.

()ne of the objects of this invention is a provision of a radio circuit which is highly efiicient in operation and which is productive of high quality and volume.

Another object of this invention is a provision of a radio circuit employing audions 10 having a plurality of electrodes including a grid which is dielectrically shielded from the other electrodes.

' A still furtherobject of this invention is a provision of a circuitemploying audions of the above type which do not require the use of a grid bias because the grid is shielded from the other electrodes.

A further object of this invention is to reduce the internal impedance of the audions by elimination of the use of a C voltage;

An additional object of this invention is to operate circuits employing audions with dielectrically shielded grids so that lower plate voltages are required resulting in an increased plate current fluctuation with a given grid voltage variation. V

A still further object of this invention is to eliminate in circuits of this type distortion due to the flow of grid current which is prevented by dielectrically isolating the grid. 0

Another object of this invention is to include a capacitance in the grid circuit to prevent direct current flow.

An additional object of the invention is to shuntthat capacitance by high resistance to prevent the accumulation of too high a charge on the grid.

These and other objects, as will appear from the following disclosure, are secured by means of this invention.

This invention resides substantially in the combination, construction, arrangement, relative location of parts, steps and seriesoi steps, all as will be described in greater detail hereinaftcr.

Referring to the drawings:

Figure 1 is a diagrammatic illustration of the princples of this invention as applied to a two stage audio amplification.

Figure 2 is a modified form of circuit in which the principles of this invention have been applied to a radio frequency amplifier.

In the operation of radio circuits employing a plurality of multi-electrode audions especially in amplifying circuits, it is at present generally necessary to employ some form of gridbias in order to prevent distortion and to improve the quality of output of such apparatus. The purpose of this invention is to secure high quality reproduction from apparatus of this nature in which a grid bias is not required. In general, this object is attained by dielectrically isolating the grid of the audions from the other electrodes preventing electrons from the cathode and plate from flowing back to the grid, thus preventinga grid current flow. A small'condenser may be employed in the grid return lead to prevent the flow of direct current which further reduces distortion.

it better understanding of this invention will be had by reference to the drawings in which Figure 1 is a diagrammatic illustration of the elements and their association to form 7 grid is of no importance in connection with this invention. Some of the forms which such a tube may assume are disclosed in my co-pending applications, Serial No. 404,002, filed November 1, 1929, and Serial No.

411,408, filed December 4, 1929.

The audion 4 is shown provided with a cathode 7 and a plate electrode 8. The cathode leads are. shunted by a high resistance 20 and the grid return lead is adjustably connected thereto. The plat-e 8 is connected to one terminal of a primary winding 10 of transformer 9 which has its other terminal connected in the usual manner of the positive side of the plate current'source. One terof l t i material 3 quency amplifiers.

minal of secondary winding 11 is connected to grid 13 of audion 12 which is also dielectrically shielded as on 14. This audion is provided with a cathode 16 which is shunted by the potentiometer 21. The plate of this audion is connected to one terminal of the primary winding 18 of audio transformer 17 which has its other terminal connected to the positive side of the plate current source. The terminals of the secondary winding 19 are connected to any suitable work circuit, as for example, the input of another amplifier stage or the terminals of a loud speaker.

In the operation of this circuit by reason of the dielectric isolation of the grids of the audions from the other electrodes, the electrons cannot reach the grid and hence an undesired grid current flow is prevented without the use of a grid bias. As a result, practically no distortion occurs, and furthermore a lower plate potential may be used and the internal impedance of the tube is greatly reduced.

In the modified form of device shown in Figure 2, the input circuit of the audion 4:2 is provided with a coupling inductness connected to the grid 13 and shunted by a variable condenser ll. The return lead of the grid includes a condenser 48 which is bridged by a high variable resistance 49. The cathode is shown at 44L and the plate at 45. The grid is shown diagrammatically as isolated from the other electrodes by the wall The plate 15 is connected to one terminal of the primary 46 of a transformer which has its other terminal connected to the positive side of the plate current supply. Consequently, 1-7 is connected by the terminals 50 to any work circuit. The circuit of Figure 2 is disclosed as a radio frequency amplifier, but the principles of this circuit may of course be applied to audio fre- The condenser 48 when the circuit is an audio circuit, may have a capacity of from 0.001 to 0.1 microfarads and the resistor may have a range up to 100,000 ohms.

In a radio frequency circuit, the condenser may have a smaller capacity and the resistor a higher resistance. In this form of circuit the grid is dielectrically isolated from the other electrodes of the audion and further isolated by means of the condenser 48. The resistor prevents the accumulation of too high a charge on the grid. The capacity 48 is so chosen that there is no appreciable selection of frequencies due to its presence. It will in fact tend to balance the induction effect of the transformer eliminating a further cause of distortion. This condenser readily passes the signal currents, but the grid may vary from positive to negative values with respect to the filament without distortion, and will be normally positive with respect to the filament. After stable operation has been established, the resistor may be fixed. With a circuit of this construction a much lower plate voltage on the tube may be employed and the same grid voltage fluctuations in the grid circuit cause an increased plate current flow. The transformers used will no longer need to match the tubes in impedance since the internal impedance of the tube is greatly reduced by elimination of a G voltage.

I am, of course, well aware that changes in the details of construction and operation of this invention may be made without departing from the principles of construction and operation, and I do not therefore desire to be strictly limited to the disclosure as given for purposes of illustration, but rather to the sketch of the appended claims.

lVhat I seek to secure by United States Letters Patent is:

1. In an apparatus of the type described, the combination comprising a plurality of multi-electrode audions each including a control electrode, input and output circuits for each of said audions electrically associated to form an amplifier, means within the audion for dielectrically isolating the control electrodes of each audion to eliminate grid current flow, and means externally of the audions in the input circuits for dielectrically isolating the control electrodes.

2. In an apparatus of the type described, the combination comprising an audion having a grid plate and cathode, and input circuit connected to said grid and cathode, an output circuit connected to said plate and cathode, a; condenser in the grid return lead, and means for dielectrically isolating the grid from the plate and cathode.

In testimony whereof I have hereunto set my hand on this 3rd day of December A. D

1929. I a -2 FREDERICK IV. HOCHSTETTER. 

